The invention is in the field of processes for preparing fibrous webs. Preferred embodiments of the invention are in the field of melt-blown and spun-bonded fibrous webs.
The prior art has provided numerous processes for preparing fibrous webs from thermoplastic materials such as polypropylene, polyethylene, polyvinyl alcohol, polylactic acid, and nylons. In many instances, fibrous webs are prepared via weaving of preformed fibers; in other instances, non-woven fibrous webs are prepared via a process such as melt blowing, spun-bonding, and melt-spinning. Innumerable variations of these processes have been provided in the prior art to produce fibrous webs suitable for use in the manufacture of many products.
Some non-woven fibrous webs are useful in the manufacture of clothing. In this regard, it has been known for some time that it is useful to incorporate a temperature stabilizing agent, such as a so-called xe2x80x9cphase change materialxe2x80x9d or xe2x80x9cmoderate temperature phase change material,xe2x80x9d into an article of clothing to provide temperature stabilization. Moderate temperature phase change materials are substances, which undergo a change in phase at a temperature of about 60xc2x0-90xc2x0 F. Because of the well-known thermodynamic principle that a phase change occurs at constant temperature, such materials are useful in preventing heat loss from the body as ambient temperature drops, and conversely, in preventing heat gain to the body as ambient temperature rises. Examples of the use of such moderate temperature phase changes materials are reported in numerous documents, for instance, U.S. Pat. No. 4,856,294, which purports to disclose a vest made with such phase change materials; U.S. Pat. No. 5,366,801, which purports to disclose a fabric containing microcapsules of phase change material; U.S. Pat. No. 5,415,222, which discloses a xe2x80x9cmicroclimatexe2x80x9d cooling garment comprising a vest which contains a xe2x80x9cmacroencapsulatedxe2x80x9d phase change material contained within a honeycomb structure, and U.S. Pat. No. 6,120,530, which purports to disclose a passive thermocapacitor for cold water diving garments.
Known moderate temperature phase change materials are conveniently provided in microencapsulated form. The microcapsules of phase change material may be secured to a substrate with the use of a binder, as is purportedly taught in a number of prior patents, including U.S. Pat. No. 5,955,188; U.S. Pat. No. 6,077,597; and U.S. Pat. No. 6,217,993. Alternatively, in the preparation of a fibrous substrate, the microcapsule may be dispersed within a polymeric melt, and fibers may be blown or otherwise prepared from the melt, as is purportedly taught in U.S. Pat. No. 4,756,958. Both of these prior art approaches suffer from a number of drawbacks. Although microcapsules can be secured to a substrate with a binder, this approach is unsatisfactory, because it is believed that microcapsules are susceptible to being debound upon washing or wear of the fabric thus made. Moreover, while in theory these problems are mitigated by incorporating microcapsules into the polymeric melt used to prepare the fibers, it is believed that in practice the microcapsule chemistry is incompatible with the temperatures required to process many thermoplastic polymers. In particular, it is believed difficult to obtain non-woven nylon or polypropylene fabric using such techniques.
It is a general object of the invention to provide, at least in preferred embodiments, a process for incorporating moderate temperature phase change materials into non-woven fibrous webs that is different from the processes heretofore described. In highly preferred embodiments, the invention has as an object to provide nylon and polypropylene non-woven fibrous webs that incorporate microencapsulated materials, and in particular microencapsulated moderate temperature phase change materials.
It is now been found that an adherent, such as a microencapsulated moderate temperature phase change material, can be incorporated into a non-woven web during a melt-blowing or a spun-bonding manufacturing process. In the melt-blowing operation, fibers are melt-blown from a polymer melt of a thermoplastic polymer. After the fibers are formed, they remain at an elevated temperature for short period of time, during which time the fibers remain tacky. In accordance with the invention, the adherent is caused to be contacted with the fibers while they are in the tacky state to cause the adherent to adhere to the fibers. In conventional melt-blowing operations, the tacky fibers are cooled with a cooling spray, which comprises a cooling fluid (typically water). In accordance with the preferred embodiment of the invention, the microencapsulated phase change material or other adherent is provided as a suspension in this cooling spray. After the hot fibers have been cooled with the cooling fluid, the fibers are collected to thereby form a fibrous web.
The invention also contemplates other web forming operations, such as spun-bonding. In a typical spun-bonding operation, fibers exit a spinarette and travel as a body to a subsequent heating stage, at which the fibrous body is heated to enhance interfiber cohesion. Most typically, the body of fibers is heated via a hot calendar or embossing roll. After exiting the heating stage, the body of fibers is tacky, and the adherent can be then caused to be contacted with the body of fibers to thereby cause adherence to the body. Even more generally, a preformed body of fibers can be heated and contacted with an adherent, which may be a microencapsulated moderate temperature phase change material or other temperature stabilizing agent, or, more generally, any other microencapsulated material, to cause the adherent to adhere to the body of fibers.
Other features and embodiments of the invention are discussed hereinbelow and in the appended claims.